Remote fiber test systems: relying on a lot more than luck

Sept. 1, 2001
SPECIAL REPORTS / Fiber and Cable

An Irish telecom operator differentiates its network's performance from the competition with continuous remote monitoring.


One of Ireland's largest telecommunications operators decided last year to install a remote fiber test system (RFTS) on its 4,000-km network, which consists of a fiber backbone and submarine cables. The carrier, Esat, a member of the British Telecom group, provides business and residential telecom services throughout Ireland-voice, data, and Internet access on broadband LAN, DWDM, SDH, ATM, and IP networks. Esat is the largest provider of corporate Internet services in the country; the carrier has about 138,000 Internet customers, 800,000 mobile customers, 16,000 corporate customers, and 100,000 residential phone customers.

Esat wanted a system that could monitor both land and submarine cables continuously and was flexible enough to expand with the network. "The DWDM and SDH equipment flags fiber failures as they occur, but this equipment does not locate the break accurately," says Derek Cassidy, Esat project manager. "If a break or degradation occurred in the fiber, we had to send engineers with OTDRs [optical time-domain reflectometers] to investigate.

The RFTS chosen by Esat, Atlas from Acterna, provides 24-hour monitoring allowing automatic detection and localization of cable damage as well as warning for slow degradation over time before traffic is affected. It consists of a series of compact, remote test units (RTUs) installed at strategic points throughout the network and a central server where data is collected and analyzed. Powerful software provides a wide range of data analysis and network-management functions.
This map of the Esat fiber-optic network, which includes terrestrial and submarine elements, shows the location of the Dundrum Engineering Center in Dublin, where the remote fiber test system's server is located.

Acterna won the Esat order in competition with other RFTS suppliers. "We chose Atlas on the basis of the quality of the system and because of the excellent technical support we received from Acterna," says Cassidy.

Phased installation of the RFTS is nearly completed. When it is finished, Esat will have a total of 10 RTUs on the backbone (seven are already installed) as well as four on the two submarine cable links to the United Kingdom.

The RFTS setup is based on a central server and two client stations. The server is located in Esat's Engineering Center in Dundrum, Dublin, which is operational 24 hours a day, seven days a week (see Figure). The client stations are located in the Network Management Center (NMC) in Dublin and the Engineering Center.

The RTUs are installed at strategic land locations around the country and at the submarine-cable stations. These locations were chosen based on information collected during an in-depth survey of the network-and with advice from Acterna. The goal was to cover the entire 4,000-km network with the minimum number of units required. For the submarine cables, and many of the land cables, there is "cross-over testing" using an RTU at each end of the cable to test in both directions.

The RFTS monitors the physical and optical layers of the fiber network from a single, standalone RTU platform. The OTDR module for the RTU provides monitoring for all types of fiber-optic networks from metro to very-long-haul. The measured trace is compared with a reference trace. If user-defined limits are exceeded, an alarm message is routed automatically to the maintenance supervisor.

The WDM module for the RTU provides all the test functions needed to analyze the quality of a DWDM network of up to 50-GHz channel spacing, alerting the operator in event of low power, a missing channel, or network degradation beyond user-defined limits. The field data is used to automatically generate a comprehensive network schematic.

Esat's RFTS is accessed via a standard Web browser. A series of user-defined codes and passwords ensures the security of the system, with a range of privileges assigned from the server station. The use of the industry-standard simple network-management protocol (SNMP) and common object request broker architecture (CORBA) ensures a smooth transmission of alarm data and cable documentation to other systems.

In the event of a network problem, the RTU sends an alarm message to the central server comprising date, time, distance, and the nature of the fault. An alarm text box is flashed onto the screen and audio warnings are triggered to alert the operator. The operator has direct access to the OTDR trace and a cable schematic, on which the alarm event is highlighted.

The built-in duty roster can be used to schedule work shifts and manage maintenance teams. It is easily configured using drag-and-drop techniques. The duty roster logs individual working hours and takes account of staff availability and holidays. It also stores contact information for each engineer and selects the best contact medium for each individual; short messaging system, fax, pager, e-mail, or GSM.

Esat's RFTS manages and documents the network, using a geographical information system (GIS) for the identification and labeling of each fiber and each cable. The GIS catalog includes location, year of installation, lists of any conduits or poles, details of splice locations, status, equipment service details, end-to-end view, and length.

There is a drawing tool provided for construction of a simple network schematic using the "drag-and-drop" component icons provided. Cable routings and outside plant can all be logged with their geographical coordinates for future fault location.

The RFTS continuously monitors the entire network. Each RTU has its own Cisco Systems' router, which is used to report faults back to the client stations, central server, and ultimately to the NMC.

"We have to make sure the RTUs always have a connection back to the main engineering center were the server is housed. So we use the network of the incumbent telecom company to carry the data as well as our own connections," explains Cassidy. "We simply ordered circuits from the incumbent and connected them to the RTU routers. So even in the event of a total disaster, we will still have a connection to the RTUs. Even if it means giving our competitor some business."

In the event of a fiber break, the RFTS identifies the problem and its location and notifies the NMC. A maintenance team is then dispatched to replace the fiber and repair the fault.

"Previously, if there was a problem, we would first send out a team to identify what the problem was," says Cassidy, "and if it turned out to be a fiber break, where was it located? It could take four hours or more, before repair or replacement could even start. The great thing about the RFTS is that this downtime is reduced considerably. Repair crews are sent directly to the fault instead of wasting valuable time trying to find its exact location."

The Esat network is designed for automatic rerouting in the event of a failure, so customers do not experience downtime if there is a fiber break. But if a break occurs on the backbone, it is in everyone's interest to get it repaired as quickly as possible.

Fiber breaks in the undersea cable are less common, but much more costly to repair. If a break is identified, a call is made to ACMA (Atlantic Cable Maintenance Agreement) within minutes of the cable failure. ACMA represents an agreement between all the cable operators that have submarine cable in the Atlantic and surrounding waters to share the purchase and running costs of the cable ships. After ACMA is notified, a repair ship is mobilized and it comes under the control of the Esat repair team, which specializes in fiber and submarine breaks. A repair starts as soon as possible.

The RFTS has reduced the callout procedure to hours or even minutes. Pre viously, it might have taken as much as a day or longer to identify and locate the failure. Now, the ship can be mobilized as soon as the RFTS flags the problem.

In addition to improving the speed and cost of network repairs, the RFTS plays a key role in the network's preventive maintenance. The system can be programmed to perform regular proactive maintenance cycles on the fiber network. In this mode, the RTUs perform a detailed scan of the fiber links for signs of degradation and component aging. The information can then be used to generate customer and management reports.

"We can track degradation and make repairs and upgrades before the problems occur," explains Cassidy. "In this way, we can optimize performance, ensuring the quality of the network for our customers."

Esat is the first Irish operator to employ RFTS for its network. "This is a key differentiator for the Esat network," says Cassidy, "because no other provider in Ireland can offer this level of performance monitoring."

Enzo Di Luigi is the fiber-optic general manager at Acterna (Sainte-Etienne, France).